Heme oxygenase substrate specificity

FIGURE 2 Proposed dual mode for calmodulin (CaM) control of nitric oxide synthase (NOS) electron transfer. Neuronal NOS is composed of a reductase and an oxygenase domain, shown as two circles. CaM binding to NOS activates at two points in the electron transfer sequence (1) It increases the rate at which NADPH-derived electrons are transferred into the flavins, and (2) it enables the flavins to pass electrons to the oxygenase domain of NOS. Activation at the first point is associated with an increase in reductase domain-specific catalytic activities, such as electron transfer to cytochrome c or ferricyanide (FeCN ). Activation at the second point is associated with a reduction of NOS heme iron, an initiation of NO synthesis from L-arginine (Arg), or a reduction of Oj to form superoxide (O2) in the absence of substrate. FAD, Flavin-adenine dinucleotide FMN, flavin mononucleotide NO, nitric oxide. 

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